Police on Thursday identified the man who killed four people at a medical center in Tulsa, Oklahoma, saying he targeted a physician whom he blamed for ongoing pain after a recent back surgery.

The gunman, identified as Michael Louis, of Muskogee, Oklahoma, died from an apparent self-inflicted gunshot, police said. 

The four victims — two physicians, a receptionist, and a man visiting a patient — were found with the suspect’s body on the second floor of a St. Francis Health System building, said Tulsa Police Department Chief Wendell Franklin.

A letter was found on Louis that “made it clear that he came in with the intent to kill Dr. Phillips and anyone who got in his way,” Franklin said.

WHAT WE KNOW ABOUT THE SHOOTING:Gunman that killed 4 targeted doctor

Here’s what we know about the suspect:

Who was the gunman in the Tulsa shooting?

Police identified the suspect Thursday as Michael Louis of Muskogee, Oklahoma.

About 30 minutes after the shooting, the Cherokee County Sheriff’s Office called the Tulsa Police Department to inform officers of a 911 call from a woman who said her husband had killed several people at the office of Dr. Preston Phillips, Franklin said. 

Police searched the suspect’s residence in Muskogee, about 50 miles southeast of Tulsa. They believed he may have planted a bomb, but the Oklahoma Highway Patrol bomb squad later found no such devices in the home, said Lynn Hamlin, Muskogee Police’s spokesperson. 

Franklin said gun tracing was used to determine that Louis purchased an AR-15-style rifle from a local gun store on June 1 and a pistol from a local pawn shop on May 29. Both weapons were fired at the scene, police said.

What was the suspect’s motive? Did he know the victims? 

The gunman shot and killed four people, including the doctor who he blamed for ongoing pain after a recent back surgery, police said Thursday. Franklin identified the four victims as Dr. Preston Phillips; Dr. Stephanie Husen; receptionist Amanda Glenn; and William Love, who was with a patient.

On May 19, Louis underwent surgery at the hospital for a back injury performed by Phillips, an orthopedic surgeon, Franklin said. After Louis’s release from the hospital, police said he called Phillips several times over the next few days to complain about ongoing pain and demand additional treatment.

On May 31, Phillips provided additional treatment to Louis before he once again called the office on June 1 to complain about back pain and request more assistance.

Police officers found a letter on the suspect after he died following the shooting, which said he intended to kill Phillips, Franklin said. 

“He blamed Dr. Phillips for the ongoing pain after the surgery,” Franklin said.